This disclosure relates to the delashing of gear assemblies.
Gear assemblies typically comprise a drivable gear (e.g., a first spur gear) engaged by a pinion (e.g., a second spur gear). Due to the manufacturing process, there are always some imperfections in the manufacturing of the teeth of the gears. Because of these imperfections, a clearance is maintained between the teeth of the driveable gear and the teeth of the pinion when the two gears are engaged. This clearance, which is also known as backlash, permits relative motion between the drivable gear and the pinion. If the clearance were not maintained, load bearing gears would not be able to operate because the meshing of the teeth between the gears would become so tight (due to the imperfections) that, even absent any deflection of the teeth, the gears would bind and cause the gear assembly to jam. In a gear system with any degree of backlash, in many applications, an audible noise is produced by the movement of the teeth of one gear through applicable backlash and into contact with the teeth of the other gear. Backlash also results in lost motion when one gear is turned through the backlash with no transmission of motion or torque to a second gear.
In the design and manufacture of compact, bi-rotational gearboxes, a first spur gear is engaged with a second spur gear. Both gears are typically fabricated from metal and are configured such that the teeth of the first spur gear are aligned with spaces defined by the teeth of the second spur gear. The teeth of the first spur gear are usually aligned with spaces defined by the teeth of the second spur gear such that clearance exists in the meshing of the teeth of each gear. Furthermore, because of the high stiffness of the metallic teeth, the surfaces of the flanks, and the need to maintain the clearance, one flank surface of each tooth of the pinion engages one flank surface of each tooth of the driven gear to result in single flank contact. Systems using single flank contact typically employ a contact area uniformly distributed across the surfaces of the engaged flanks. The uniformly distributed contact area, in conjunction with the clearance between the engaged teeth, is a factor that contributes to the audible noise produced during the driving of the first spur gear by the second spur gear. In addition, there is also audible noise during periods when the rotational direction of the first spur gear is reversed to reverse the direction of rotation of the second spur gear.
Such noise, although not indicative of a defect in the gear assembly, generally proves to be undesirable, especially when the gear assembly is located within or in communication with the passenger compartment of a motor vehicle. In addition, there is also vibrational feedback that may occur from the driven portion back to the driving portion. This vibrational feedback can set up a resonance in the steering system. Thus, because of the backlash in the gear assembly, there can be a resonance or rattle felt by the driver at the hand wheel.
The reduction of backlash and the minimization of noise have been achieved in worm gear assemblies. In such assemblies, the worm gear is made completely of a polymer element. Such an arrangement in the worm gear assembly is preferable due to the complexity of the gear and also because the load is not as high as with the spur gear assembly. Thus, when a gear is made completely of a compliant material, such as the worm gear, those gears are limited as to the amount of load that the gear can handle. It is desirable for spur gear assemblies to carry higher loads than is usually carried by worm gears and thus, it may not be desirable to have a spur gear made completely from a compliant material.
The reduction of backlash and the minimization of noise have been achieved in the related art of instrument gearing. In that type of gearing, backlash has been minimized through the use of split gears, which typically comprise two gear halves mounted side-by-side and wherein each gear half includes a plurality of teeth. A spring is positioned between each gear half to bias each gear half in opposing rotational directions. The opposing rotational directions cause flank surface contact to be maintained between a tooth on one of the gear halves and a tooth of a gear with which the split gear is in contact while simultaneously causing flank surface contact to be maintained between the aligned tooth on the other of the gear halves and an opposing flank surface of the tooth of the gear with which the split gear is in contact.
Such a structure allows for double flank surface contact to be maintained between successive teeth in a gear set, which reduces or eliminates backlash in the gear set, thereby minimizing noise and lost motion. However, because of the deflection of the spring, both the contact force and the size of the contact area maintained by the teeth of the split gear on the successive teeth of the gear with which the split gear is in contact remain constant regardless of the load imposed on the gear set. The force and contact area size cause the contact pressure to vary, which thereby causes frictional forces to be experienced by the gear flank surfaces as the load varies. Such frictional forces in turn cause a constant degradation of performance within the gear set. Moreover, such instrument gearing is generally used to indicate a position of one element with respect to another; however, instrument gearing cannot bear a significant load.
In addition, instrument gearing usually operates only in one direction and thus, instrument gearing generally does not have a problem with position feedback. Position feedback occurs when a system that operates in both a first and second direction and compliant in the first direction than in the second direction. This position feedback poses a problem with the electronics because the electronics do not like to be biased in that way.
In addition, gears generally also require some sort of bearing or bearing surface on which to rotate. Components that serve more than one function should be employed whenever possible in the interests of compactness and simplicity.